1. Field of the Invention
This invention relates to wells which are produced by means of gas lift operations, and more particularly to a gas lift valve for use in such gas lift operations.
2. Related Art and Information
Gas lift valves have been used for many years to aid in the production of oil wells lacking sufficient natural pressure to flow naturally without assistance. Such valves commonly control the admission of lift gas into the well tubing from the well casing to aid in lifting formation liquids to the surface. Lift gas is generally injected into the well casing at the surface. Several types of gas lift valves have been known. Some gas lift valves open in response to casing pressure, some in response to tubing pressure, some admit gas into the tubing continuously, others intermittently. Some gas lift valves, for instance, are provided with main valves which are pilot actuated, that is, when their pilot valves open, their main valves are caused to open, and when their pilot valves close, their main valves close in response thereto. The pilot valve may respond to casing pressure or to tubing pressure or to the difference between those two pressures.
Listed here are certain U.S. patents which disclose prior gas lift valves which may be pertinent to the invention disclosed and claimed in this present application.
______________________________________ Re. 25,292 2,994,335 3,086,593 3,125,113 3,183,922 3,311,126 3,311,127 ______________________________________
U.S. Pat. No. 2,994,335 issued to W. A. Dudley on Aug. 1, 1961 and its reissue Patent Re. 25,292 issued on Dec. 4, 1962, disclose a gas lift valve which has a pilot valve with a bellows and spring, the spring for biasing the pilot valve toward closed position and the bellows, exposed to casing pressure for moving the pilot valve toward open position. When casing pressure rises to a predetermined value the bellows lifts the pilot valve to open position in opposition to the spring. When the pilot valve opens casing pressure enters through the pilot valve to act upon the main valve and move it to open position against the force of its spring to allow transfer of lift gas into the tubing. When the casing pressure falls below a predetermined value the pilot valve will close and this will result in the main valve closing, it being moved by its spring.
U.S. Pat. No. 3,086,593 which issued on Apr. 29, 1963 to C.B. Chitwood discloses a gas lift valve having a pilot valve including a bellows attached to the pilot valve member and charged with a compressed gas. The bellows hold the pilot valve on its seat (closed) when the casing pressure to which it is exposed is below a predetermined level. When the casing pressure rises above such predetermined level, the bellows will be compressed and will unseat (open) the pilot valve. Opening the pilot valve allows casing pressure to move the main valve to open position against the compression of its spring. When casing pressure falls below the predetermined level, the pilot valve closes, whereupon the main valve is returned to closed position by the spring.
U.S. Pat. No. 3,125,113 issued to C.P. Lamb, et al., on Mar. 17, 1964. This patent discloses a gas lift valve which is controlled by a pilot employing a bellows 37 (FIG. 1A) and 76 (FIG. 3). When pressure exterior of the bellows compresses the same, the pilot valve 75 is lifted off its seat 74 and casing pressure passing through the open pilot valve and through passage 77 into chamber 67 to act upon piston 66 to open main valve 65.
U.S. Pat. No. 3,183,922 which issued May 18, 1965 to C.P. Lamb, et al., discloses a pilot operated gas lift valve. The pilot valve (ball 72) is held on seat 71 by pilot spring 74 and bellows 63. The bellows is exposed to tubing pressure conducted thereto through outlet 21, main valve stem bore 34, and passage 62. Casing pressure is communicated to the ball and seat via passage 59. When casing pressure increases to a predetermined value, ball 72 will be unseated and casing pressure flowing through the seat will pass through passage 62 and will be applied to piston 35 to thus move it down in opposition to main valve spring 44. Main valve 48 attached to the piston will thus be unseated and moved to its open position. When the casing pressure falls to a predetermined value, the pilot spring and the bellows will return the ball 72 to its seat to bar further entry of casing pressure. This will allow tubing pressure to equalize on upper and lower sides of the piston and permit spring 44 to close the main valve.
U.S. Pat. No. 3,311,126 which issued to William A. Dudley on Mar. 28, 1967 and discloses a pilot operated gas lift valve. This device has a pilot valve 60 which engages seat 70. Pilot spring 75 biases the pilot valve towards its seat. A bellows 72 is also connected to the pilot valve. Port 69 communicates casing pressure into the pilot valve chamber. When casing pressure reaches a selected level, the bellows 72 compresses, overcomes spring 75, and lifts pilot valve 68 off its seat. Casing pressure then flows through seat 70 and its passage 71 into the chamber (47) therebelow where it acts upon piston (18). The piston is thus depressed, compressing spring 55 and opening the main valve 17 to permit flow of lift gas from the casing into the tubing through inlet screen 38, inlet ports 37 and through bores 42 and 43, to exit through outlet ports 39. When the casing pressure falls below the selected level, pilot valve 68 closes, chamber (47) is shut off from the casing pressure and becomes equalized with tubing pressure, the excess pressure bleeding to the tubing through bore 64 of the piston (18) and its stem 17. With pressures equalized above and below the piston, main valve spring 55 moves the main valve to closed position.
U.S. Pat. No. 3,311,127 issued to William A. Dudley on Mar. 28, 1967 and discloses a pilot operated gas lift valve in which two pressure responsive members 35 and 53 are used as bellow-phragms to contain an incompressible liquid therebetween. This liquid is metered through adjustable needle valves to control the length of time that the gas lift valve remains open before it closes. This patent is not believed to be pertinent to the instant application.
No pilot operated gas lift valve was found in the prior art having a diaphragm subject to lift gas pressure and functioning to unseat the pilot valve to cause opening of gas lift valve.